Laminated veneer lumber (LVL) is a wood composite product made by laminating selected veneers in a parallel alignment. In conventional LVL manufacturing processes, round logs are slashed and heated, and then veneer is peeled, clipped, and dried. The veneers are then graded and sorted based on quality. After grading, large billets of LVL are laid up and pressed using a highly automated process. LVL billets are produced by applying layers of veneer and adhesive sequentially to a moving belt. The applied adhesive between each layer of veneer is commonly referred to in the industry as a “glue line.” After lay-up, some mills prepress the LVL billets in a cold press prior to final pressing in a hot press.
LVL hot press methods fall into two primary categories: continuous press processing and fixed length press processing. Both press methods are limited by the adhesive cure speed in the innermost or core glue line. Typically, temperatures for curing the core glue line are in a target range of about 225° F. to about 240° F. for complete cure. Heating the core glue line to a lower temperature may lead to delamination and separation of the laminate by lack of adhesion. Heating the core glue line to a higher temperature may result in “heat blows” whereby steam pressure literally separates the bonded layers making the product useless.
The time required to achieve a temperature within the target range is dependent upon a number of material and process variables. Accordingly, many LVL facilities must limit production due to press limitations and speed of production. Some facilities have experimented with increasing the temperature of the platens on presses to accelerate the time required to achieve a temperature within the target range, but this practice may lead to wood degradation, delamination, and heat blows. The use of microwave pre-heaters may improve throughput when billets are pre-heated to a temperature below the target range before hot pressing, but this increased production may also come with higher capital requirements, energy costs, and process complications.
The production limitation challenges discussed above with respect to LVL manufacturing facilities also apply to manufacturing processes for other wood composite products. Thus, there is a need to develop new systems and methods for manufacturing wood composites to overcome capacity limitations. Ideally such systems and methods would enable an increased through-put for production of wood composite products without the drawbacks of other known methods.